Currently, various kinds of systems for performing a communication by phase-modulating an information transmission signal by using a spreading code are put in practical use. As one of systems using such a communication method, there is a GNSS. For example, in the GPS that is implemented by U.S.A, it is used for positioning and the like by transceiving an L1 signal and an L2 signal formed by phase modulating with a PN code (C/A code or P code), an L1 carrier wave and an L2 carrier wave superimposed with a navigation message.
As one of systems of such a GNSS, there is the Galileo that is expected to be implemented by Europe. In the Galileo, as disclosed in Nonpatent Document 1, a CBOC signal is used. The CBOC signal is, upon using a carrier wave same as the GPS and a PN code different from the GPS, a signal of which the PN code is further modulated by a synthesized subcarrier constituted by synthesizing a BOC(1, 1) subcarrier with a BOC(6, 1) subcarrier by a particular synthesizing ratio. Specifically, the particular synthesizing ratio is BOC(1, 1):BOC(6, 1)=10(1/2):1 in electric power ratio.
Note that, due to a code of BOC(6, 1) at the time of synthesizing, a CBOC. in-phase signal (E1B signal) and a CBOC. anti-phase signal (E1C signal) exist. In the following explanation, the CBOC. in-phase signal is simplified as the “CBOC+ signal” and the CBOC. anti-phase signal is simplified as the “CBOC− signal.” Further, when referring to the same thing for both of the CBOC+ signal and the CBOC− signal, they are simply referred to as the “CBOC signal.”
Further, a receiver of the Galileo generates a replica code based on a PN code and a subcarrier that are used on a transmission side, and demodulates the replica code by performing correlation processing of the to replica code and a received signal to perform a code tracking. For example, in the receiver for the Galileo, a CBOC replica code constituted by synthesizing the BOC(1, 1) subcarrier with the BOC(6, 1) subcarrier at a synthesizing ratio according to its use is used for the correlation processing.